The hypotheses that suckling behavior is related to the month-specific rate of menstrual cycle recovery will be tested along with alternative hypotheses that the length of postpartum amenorrhea may be influenced by such factors as maternal weight/height ratio, fatness, age, parity, ethnicity, educational level or socio-economic standing. The project is viewed within the larger context of the health benefits of breastfeeding for infants and their mothers, as well as any community and family benefits which may result from suckling-induced postpartum infecundity. A proportional hazards model for time-dependent covariates will be applied to the data collected from a population of 120 breast-feeding women and a control group of 30 bottle feeding mothers. Time-series suckling data will be recorded by study subjects with the aid of a microprocessor-controlled electronic recording device to be developed and fabricated as part of the scope of the project defined by this application. Menstrual history data will be recorded by the subjects and these, as well as electronic data, will be collected during monthly field interviews. The population base under study is a four-county area of North-eastern New Mexico of 32,546 people. The ethnic composition of the region is 80.9% Hispanic, 18.7% Anglo and 0.4% American Indian and other. The median family income of these four counties is under $11,000.